The SVG Group Element is used to group SVG Elements together (much like a container)

There are two main reasons to use the SVG Group Element - for grouping SVG Elements and for doing transformations to the coordinate space the SVG Elements are in

Any transformation applied to the SVG Group Element is applied to all of the child elements contained inside

The transformations you can perform on the on the SVG Group Element are based on Linear Algebra

The SVG Group Element Translate transformation allows you to move all of the elements inside of the <g> ... </g> a certain numbers of units in the X direction and a certain number of units in the Y direction

At a deeper level, what the SVG Group Element transform is doing is transforming the SVG Coordinate Space